As shown in FIG. 1, a Chinese Utility Model with patent No. 200820071126.8 discloses a “big-screen infrared monitoring projection objective” which includes two focusing devices, i.e., a projection focusing device 17 and a monitoring focusing device 19, for solving focusing problems of a projection objective and an infrared monitoring objective. That is, the projection objective and infrared monitoring objective of this patent need to be focused separately.
The labels in FIG. 1 represent as follows: single negative lens 1, single negative lens 2, single negative lens 3, single positive lens 4, light splitting prism 5, single positive lens 6, single negative lens 7, balsaming lens 8, balsaming lens 9, single positive lens 10, filter 11, single positive lens 12, single negative lens 13, single positive lens 14, balsaming lens 15, projection lens barrel 16, projection focusing hand wheel 17, flange 18, monitoring focusing hand wheel 19, monitoring lens barrel 20, flange 21, CMOS chip 22, chip fixed plate 23, field diaphragm 24.
When projection distance changes, the projection focusing device 17 needs to be adjusted for focusing of the projection objective, i.e., pushing the projection lens barrel 16 and the flange 18 to move back and forth as a whole, so as to make focused projection image clear. Because the infrared monitoring objective mounted on the projection lens barrel 16 moves synchronously, the focusing device 19 thus needs to be adjusted to make the infrared monitoring objective be focused, such that images collected by the CMOS chip 22 meets requirements of interactive operation.
Such projection system needs focusing twice, which is inconvenient in operation. In addition, the projection image is formed by visible lights, users can determine whether the focusing is clear by eyes, but the infrared monitoring image is formed by invisible infrared light, and the eyes cannot determine whether the requirements of interactive operation are met.